The present invention relates to a graphic display apparatus having a graphic memory and, more particularly, to a graphic memory interarea data transfer system for copying data at one area of a graphic memory into another area in the memory.
A graphic display apparatus of the type described above generally has a CRT monitor 11 for graphic display, a graphic memory (GM) 12 for storing graphic data (i.e., pattern data) to be displayed on the CRT monitor 11, a microprocessor (.mu.P) 13 for controlling the overall apparatus, and a graphic control unit (GCU) 14, as shown in FIG. 1. The GCU 14 serves as an interface between the GM 12 and the .mu.P 13. The GCU 14 has a CRT controller (not shown) for performing display control for the CRT monitor 11. The GCU 14 also has an X address counter 15 and a Y address counter 16 for performing a read/write operation of graphic data for itself. The X and Y address counters 15 and 16 count an X coordinate (X coordinate address) and a Y coordinate (Y coordinate address) on a display screen of the CRT monitor 11. An address of the GM 12 is designated by linked information of these X and Y coordinate addresses.
In a graphic display apparatus of this type, as shown in FIG. 2, in order to shift a screen portion, it is sometimes desired to copy or move n continuous display data at, for example, coordinates (XO, YO), (XO+1, YO), . . . and (XO', YO) (where XO'=X+n-1) of the screen of the CRT monitor 11 to a region defined by coordinates (X1, Y1), (X1+1, Y1), . . . and (X1', Y1) (where X1'=X1+n-1). In such cases, the .mu.P 13 first sets the coordinates XO and YO in the X and Y address counters 15 and 16 and generates a read request of the GM 12 to the GCU 14. Then, the GCU 14 transfers the contents XO and YO of the X and Y address counters 15 and 16 to the GM 12, thereby requesting data read. As a result, graphic data corresponding to the coordinates XO and YO is read from the GM 12 to the GCU 14. The GCU 14 transfers the graphic data from the GM 12 to the .mu.P 13. Subsequently, the .mu.P 13 sets copy destination coordinates (addresses) X1 and Y1 in the X and Y address counters 15 and 16 of the GCU 14. While the .mu.P 13 transfers the received graphic data to the GCU 14, it supplies a write request of the GM 12 to the GCU 14. Then, the GCU 14 transfers the contents X1 and Y1 of the X and Y address counters 15 and 16 to the GM 12 and writes the above data (graphic data at the coordinates XO and YO) in the GM 12. In a similar manner, a read operation of graphic data at coordinates XO+1 and YO, a write operation of the readout data at coordinates X1+1 and Y1, . . . , a read operation of graphic data at coordinates XO' and YO, and a write operation of the readout data at coordinates X1' and Y1 are sequentially performed. In this manner, a designated copy operation is completed.
In conventional data transference in a graphic memory, the read/write operation of graphic data to be transferred is performed in a point-to-point manner. For this reason, the data transfer speed is limited by the speed of the .mu.P, so that a high-speed data transfer cannot be performed.